The use of bone substitute materials are common practice in orthopaedic surgical procedures for the filling of bony voids or to treat bone defects. These materials, following implantation, may resorb and be replaced by new bone as they do so. Bone substitute materials can be formulated as a paste that can be injected or digitally packed into open bone voids where they are allowed to cure in situ, or alternatively they can be moulded into solid implantable devices that can be packed into bone voids that are not intrinsic to the stability of the bony structure. It is important to ensure that the bone void does not become pressurised during insertion of the bone substitute material. This is particularly difficult to achieve if the bone void or defect is closed or contained.
Certain bone substitute materials are now increasingly being used to release therapeutic agents into bone void sites. These bone void sites may, for example, be infected sites and the therapeutic agents may be antimicrobials. Alternatively the medical condition may be a void created by a tumour and the therapeutic agent may be an antineoplastic or antiresorptive agent. Further, the therapeutic agent may stimulate new bone growth and be incorporated into the bone substitute material to enhance its osteogenic potential.
There are several methods in which surgeons will facilitate the placement of bone substitute material within a bone void or IM canal. For example, surgeons may inject a high viscosity bone substitute material into the bone void or IM canal until the void or IM canal is filled to its capacity with said bone substitute material.
Another method used by surgeons is to digitally pack a bone substitute material into the void again until said void is completely full.
This manner of placing the bone substitute material within a void and more specifically within the IM canal is known to increase the pressure within the void such that the increased pressure may result in an embolism, such as a fat embolism. Fat embolism syndrome (FES) is caused by fat droplets which are then found within the peripheral and lung microcirculation1. FES is a serious complication and can result in the death of the patient.
The pathologic significance of FES was first noted in 1862 by Zenker; however the first person considered to diagnose fat embolism was Von Bergmann in 1873, who reported on his findings concerning this condition1,4.
As we are an aging population it means that the number of orthopaedic operations involving bone voids and more specifically the IM canal are increasing, thus increasing the risk of embolization or FES which in turn means an increase in perioperative cardiorespiratory emergencies1.
Patients suffering from FES may be asymptomatic for a period of 12 to 48 hours before the clinical manifestations of the syndrome; these manifestations include but are not limited to tachycardia, petechial rash, elevated temperature (usually in excess of 38.3° C.), hypoxemia, and also neurological symptoms6.
The mortality rate for patients suffering from FES is from 5-15%3; however proper treatment of the patient through ensuring good arterial oxygenation, the restriction of fluids and the use of diuretics which assist in minimising the accumulation of fluid in the patients lungs will assist in recovery.
There are several methods surgeons use to minimise pressure increases within a void or the IM canal which is being filled with bone substitute material; however, these methods to decrease pressure have been found to cause additional issues for both the surgeon and the patient.
One of these methods is to use a venting hole. This is where the surgeon drills a secondary opening within the long bone which is usually placed distal to the hole which the surgeon created for the placement of the bone substitute material. However, this method of reducing void or IM canal pressure has been found to have several issues. One of these issues is that the bone substitute material which the surgeon injects or digitally packs into the long bone may escape through the venting hole. This therefore means that an insufficient amount of bone substitute material may remain within the void or IM canal. Another issue found with this technique of using a venting hole to reduce void pressure is that it can cause injury to the patient's surrounding soft tissues2 as well as increasing the risk of fracture at the site of the venting hole.
It has also been found that the use of this venting hole technique may not be sufficient on its own to maintain distal pressure below the point which would cause an embolism or the occurrence of FES5 in the patient.
Therefore, the problem being addressed by the present invention is how to effectively and safely introduce bone substitute material, with or without a contained therapeutic agent therein, into a contained bony void in a patient, such as an IM canal, while ensuring that the bone void or defect does not become excessively pressurised, thus minimising the potential for embolization of the void contents into the patients' blood-stream.